Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D239/00—Heterocyclic compounds containing 1,3-diazine or hydrogenated 1,3-diazine rings
  • C07D239/02—Heterocyclic compounds containing 1,3-diazine or hydrogenated 1,3-diazine rings not condensed with other rings
  • C07D239/24—Heterocyclic compounds containing 1,3-diazine or hydrogenated 1,3-diazine rings not condensed with other rings having three or more double bonds between ring members or between ring members and non-ring members
  • C07D239/28—Heterocyclic compounds containing 1,3-diazine or hydrogenated 1,3-diazine rings not condensed with other rings having three or more double bonds between ring members or between ring members and non-ring members with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, directly attached to ring carbon atoms
  • C07D239/30—Halogen atoms or nitro radicals

Definitions

• the present invention is directed to a method for preparation of 2-bromo-substituted pyrimidines. In particular, it is directed to the synthesis of 2-bromo-5-alkylpyrimidines.
• Pyrimidine derivatives are extremely important chemical compounds in a wide range of applications such as agrochemicals, pharmaceuticals, and liquid crystals.
• easy accessible and versatile pyrimidine building blocks are desired.
• formation of C-C single bonds via palladium catalyzed cross-coupling reactions such as the Suzuki type [N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95 , 2457-2483] is a very powerful synthetic approach for building up pyrimidine containing molecules.
• the present invention faces the problem of providing a clean and efficient preparation of 2-bromo-substituted or 2-iodo-substituted pyrimidines of general formula I.
• the method according to the invention provides the desired compound of formula I in good to high yields.
• the reaction proceeds quickly and very cleanly without cooling and does not require the use of any highly toxic reagent.
• it starts with easily accessible starting material - 2-chloro-substituted pyrimidines of formula II which are commercially available (e.g. from Avocado Research, UK, Maybridge Chemical Company Ltd., UK, Apollo Scientific Ltd., UK, and Syntec GmbH, Germany) or can be easily synthesized by methods well known to those skilled in the art - and readily available reagents.
• aqueous HBr or aqueous Hl yield at best a 1:1 mixture of starting material and the desired product of formula I which mixture cannot be separated by conventional techniques, and potassium iodide in acetone gives no product at all.
• alkyl means straight-chain and branched saturated hydrocarbon radicals with 1 to 16 carbon atoms; the hydrocarbon radicals may be unsubstituted or substituted with one or more substituents being independently selected from the group consisting of F, Cl, Br, I, OH, SH, CN, amine, NO 2 , cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and cycloheptyl.
• alkyl is also meant to comprise hydrocarbon radicals in which one or more of the CH 2 groups are such replaced by -CO-O- or -O-CO- that there are no adjacent oxygen atoms.
• alkyl is a straight-chain or branched saturated hydrocarbon having 1, 2, 3, 4, 5, 6, 7 or 8 carbon atoms and being unsubstituted or mono- or poly-substituted with F. More preferably, alkyl is meant to be methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-pentyl, neopentyl, n-hexyl, n-heptyl, n-octyl. Most preferably, alkyl is a straight-chain hydrocarbon of up to 8 carbon atoms.
• alkoxy means "O-alkyl” in which the oxygen atom is directly linked to the group or ring being substituted with alkoxy and alkyl is defined as above.
• alkyl in “O-alkyl” means methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-pentyl, neopentyl, n-hexyl, n-heptyl or n-octyl, whereby alkyl is optionally substituted with F.
• alkoxy is -OCH 3 , -OC 2 H 5 , -O-i-C 3 H 7 , -O-n-C 4 H 9 , -O-t-C 4 H 9 , -OCF 3 , -OCHF 2 , -OCH 2 F or -OCHFCHF 2 .
• oxaalkyl comprises alkyl moieties in which at least one non-terminal CH 2 group is replaced by O in such a way that there are no adjacent oxygen atoms.
• oxaalkyl comprises straight-chain radicals of the formula C n H 2n+1 -O-(CH 2 ) m - in which n and m are independently of each other 1, 2, 3, 4, 5 or 6; especially n is 1 or 2 and m is an integer from 1 to 6.
• thioalkyl comprises alkyl moieties in which at least one terminal or non-terminal CH 2 group is replaced by S (sulfur) in such a way that there are no adjacent sulfur atoms; it may also be designated as "S-alkyl".
• thioalkyl comprises straight-chain radicals of the formula C n H 2n+1 -S-(CH 2 ) m - in which n is 1, 2, 3, 4, 5 or 6 and m is 0, 1, 2, 3, 4, 5 or 6; especially n is 1 or 2 and m is zero or an integer from 1 to 6.
• cycloalkyl comprises alicyclic hydrocarbon radicals with 3 to 10 carbon atoms; the alicyclic hydrocarbon radicals may be unsubstituted or substituted with one or more substituents being independently selected from the group consisting of F, Cl, Br, I, OH, SH, CN, amine, NO 2 , alkyl, alkoxy, oxaalkyl or thioalkyl, in which alkyl, alkoxy, oxaalkyl and thioalkyl are defined as above.
• cycloalkyl includes cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and cycloheptyl all of which may be unsubstituted or substituted with an alkyl radical. More preferred, cycloalkyl includes cyclohexyl substituted in its 4-position with an alkyl radical.
• aryl comprises aromatic hydrocarbon moieties; the aromatic hydrocarbon moieties may be unsubstituted or substituted with one or more substituents being independently selected from the group consisting of F, Cl, Br, I, OH, SH, CN, amine, NO 2 , alkyl, alkoxy, oxaalkyl, thioalkyl, cycloalkyl, and heterocyclyl.
• aryl includes unsubstituted phenyl or naphthyl or phenyl substituted with 1, 2 or 3 of the same or different groups being selected from F, alkyl, alkoxy, fluorinated alkoxy and cycloalkyl.
• aryl is a substituted phenyl, it is preferred to have at least a substituent in 4-position of the phenyl.
• aralkyl means an aryl being linked to the group or ring substituted via an alkyl radical.
• aralkyl means a phenyl-CH 2 -CH 2 - (phenethyl) moiety. It is preferred that aralkyl includes an aryl-ethyl moiety in which at least the 4-position of aryl is substituted and optionally one or two further positions of the aryl ring are substituted with any one of the substituents of "aryl" as described above.
• heterocyclyl comprises saturated and unsaturated heterocyclic rings including heteroaromatics; the heterocyclyl moieties may be unsubstituted or substituted with one or more substituents being independently selected from the group consisting of F, Cl, Br, I, OH, SH, CN, amine, NO 2 , alkyl, alkoxy, oxaalkyl, thioalkyl, cycloalkyl, aryl, and aralkyl.
• heterocyclyl includes pyrrolidine, piperidine, piperazine, morpholinyl, and further pyrimidine moieties all of which may be substituted.
• the halogenating agent of the present invention HX in an acid
• HX in an acid
• the exact concentration and amount of HX used are not crucial for the outcome of the reaction.
• X Br
• a solution of 30 wt.% HBr in glacial acetic acid gives excellent yields.
• HX may be used in an equimolar amount or in an excess, e.g. in a 1.1-fold or 1.5-fold up to 3-fold or even 6-fold excess.
• X in formula I and in HX is Br providing 2-bromo-substituted pyrimidines of formula I in excellent yields.
• both Y 11 and Y 12 in formulas I and II are hydrogen. Consequently, the method according to the invention then yields 2-bromo- or 2-iodo-5-substituted pyrimidines which are preferred for the synthesis of liquid crystals containing a pyrimidine ring by utilizing C-C-coupling reactions.
• R 11 in formulas I and II is alkyl or cycloalkyl. It is most preferred that R 11 in formulas I and II is a straight-chain alkyl radical.
• the acid used as a solvent for the halogenating agent HX may be any inorganic or preferably organic acid suitable to dissolve the agent HX and, preferably, the pyrimidine of formula II in order to facilitate the conversion of the 2-chloro-substituted pyrimidine.
• the acid is a carboxylic acid. It is even more preferred that said carboxylic acid is non-aqueous and selected from the group consisting of formic acid, acetic acid, propionic acid, and trifluoroacetic acid.
• the solvent may also be a mixture of two or more of said acids. Most preferred the acid is glacial acetic acid.
• the method according to the invention may be run at any temperature providing a sufficient conversion rate. It is preferred that the reaction is performed at a temperature between room temperature (about 20 °C) and the solvent's reflux temperature. It may also be useful to initiate the reaction in a reaction step (A) at a rather moderate temperature, e.g. between about 20 and about 30 or 35 °C, and to drive it to completion if necessary at elevated temperatures, preferably by refluxing the reaction mixture afterwards in a reaction step (B).
• the reaction time depends on the actual rate of the individual reaction. It may be useful to run the reaction within a period of 1 min up to 24 h, preferably within a period of 15 min up to 8 h, more preferably within a period of 30 min up to 2 h.
• reaction product of formula I prepared according to the invention's method may be isolated by usual work-up and purification with standard procedures well known to those skilled in the art. However, due to the high yields and the very clean reaction outcome, the product may also be used without further purification.
• the 2-bromo-alkylpyrimidines obtainable by use of the invention's method can be further reacted without purification with an aromatic boronic acid applying Suzuki reaction conditions in order to afford a liquid crystalline compound containing a pyrimidine moiety.
• the starting materials, reagents and solvents were purchased from Maybridge Chemical Company Ltd., UK (5-propyl-2-chloropyrimidine), Aldrich Chemical Company, US (HBr solution), Lancaster, UK (3,5-difluorophenylboronic acid; Pd catalyst), and VWR, UK.
• HPLC Hewlett Packard 1090 with a Licrospher 100 column
• GC-MS Align 5973 Detector and GC 6890

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• 2003
  • 2003-09-25 EP EP20030021622 patent/EP1411048A1/de not_active Withdrawn

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